The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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Rotational Molding Cycle Time Reduction via Exterior Mold Modification
Production cycle times for rotational molding are limited by the time required to heat up and cool down the mold and the product. Consequently, efforts have been made to enhance heat transfer to and from molds, ultimately reducing cycle times. The application of pins and roughened textures to molds has been investigated with several techniques being employed to predict the enhancement of heat transfer. To validate these predictions a series of rotomolding trials have been carried out using surface enhanced molds. Excellent cycle time reductions in the order of 30 and 20% have been achieved for the pin and roughness enhanced molds respectively, demonstrating the significant benefits mold exterior modification can provide to the industry.
Analysis of Interface of Two Layer Molded Product by Simultaneous Composite Injection Molding
Simultaneous Composite Injection Molding (SCI) is a injection molding technique to impart two layered injection molded composites, which consists of top and bottom layers, by simultaneously feeding two resins through independent cylinders. We have previously reported that low cylinder temperature and low injection speed were key parameters for producing excellent two-layered specimens, preventing commingling between the layers.In this study, the focus shall be on the interface structure in two layer molding in a molding parameter under which a desirable two layered specimen can be obtained. The used materials consist of blend of PC+ABS, a weight ratio of 6 to 4. According to high magnification SEM photos, internal structure was not observed in a region near the interface of the resin layers. Although elongated structure was observed near the mold wall, round shape was seen near the interface. The thickness of interface region was measured.
The Influence of Meeting Angle on the Weld Line Strength in Injection Molded Short-Fiber-Reinforced Polyamide 66
In this report, an experimental investigation has been conducted to examine the effect of meeting angle on the tensile strength of weld line in commercial available 33% glass-fiber-filled PA66 composites. A film gated rectangular plaque mold with circular, square and diamond inserts was used to generate weld line, and the diameter of circular insert has four sizes viz. 30,25,20,15 centimeters. The meeting angles were obtained by filling simulation package. The results showed that the strength of weld line varied linearly with meeting angle during two domains, and the critical angle was about 100°. The larger the meeting angle, the higher the strength of weld line.
Fast BEA for Cooling Analysis in Injection Molding
Boundary element analysis (BEA) is a commonly used method for the cooling analysis in injection molding. However, how to solve the BEA equation is a challenging problem when the number of elements becomes very large. With the ability of current personal computers, it seems no way to obtain accurate solution. A fast BEA solver is studied in this paper. Considering the coarse mesh is good enough in most cases, an indirect method to make dense mesh coarse is suggested, in which the elements are classified into some groups. The element-group temperature is firstly solved, and then the result is used to further calculate element temperature. The method tremendously shortens the computing time. The given example shows the result by the method is very reasonable.
Effect of Element Geometry in the Processing of Highly Filled Materials in High-Speed Deep-Flighted Twin-Screw Extruders
It is well known that deeper flights lead to improved efficiencies in a twin-screw extruder. The deeper flights result in the reduction of shear rates. This is taken advantage to increase the screw speed thereby maintaining the mixing rates and increasing the volumetric capacity of the machine. An improvement in process efficiency is realized due to the reduction in viscous dissipation per unit mass of material.The localized increase in melt temperature due to the working of the kneading elements at high speeds is still a problem. Fractional lobed element geometry with unequal tip angles can be used to solve these problems. These new geometry can easily replace standard kneading elements. These fractional three and four lobed geometry are used in the processing of highly filled LLDPE with TiO2. Melt Temperatures and Dispersive Mixing effectiveness by in-line melt filtration data are discussed while processing with the known “Erdmenger” geometry and the new Fractional geometry.
Meeting Application Requirements with Conductive Carbon Black
High structure or so-called conductive carbon blacks (CCB’s) constitute the major family of conductive additives. They enable to make polymers permanently conductive at ‘low’ to ‘very low’ loadings, for technical applications involving i.e. the transport of energy, the protection against arching or discharge. Designing conductive parts requires certain know-how as many parameters influence the final electrical conductivity, and many other requirements have to be fulfilled. This paper highlights the impact of the carbon black (CB) type and loading, the polymer type and the compounding conditions on the conductive, mechanical, dispersion and flow properties of various plastics compounds. The study especially positions a unique family of ‘low surface area (LSA)’ CCB’s, suggests means to make conductive parts with compounding and transformation ease, and points out that the more conductive additive does
Performance of Polymer Composite Gears - Effect of Tooth Deflection
Unreinforced nylon 6/6, 20 % short glass fiber reinforced nylon 6/6 and 20 % short carbon fiber reinforced nylon 6/6 materials were used for understanding the effect of tooth deflection on gear performance. Test materials were injection molded into spur gears of 2 mm module, 200 pressure angle, 17 number of teeth and 6 mm face width. A test rig is designed and developed in the laboratory to quantify the hysteresis loss of test gear with the measurement of single tooth deflection during static loading and unloading. The performance test is conducted using a power absorption type gear test rig at a constant rotational speed of 1000 rpm and at 0.8 and 1.5 Nm torque conditions. Temperature of test gears during performance tests is continuously measured using non-contact infrared temperature sensors. The net surface temperature measured in reinforced gear during testing is less than that measured in unreinforced gears. A better heat dissipation and less amount of heat generation contributes to improved gear performance.
The Effect of Gamma Sterilisation on Colour and Mechanical Performance of Medical Rigid PVC Compounds
A range of commercially available gamma sterilisable medical rigid PVC (clear) compounds were characterized for hardness, specific gravity, Vicat softening, heat stability and rheological properties. In addition, the effect of exposure to gamma irradiation at 25 and 40 kGy on the colour, mechanical performance and dynamic mechanical response of the various PVC compounds was investigated. The results show no significant difference in hardness of the materials tested. However, significant differences in heat stability, Vicat softening temperature and rheological properties were evident. The results showed that exposure to gamma irradiation had only a slight effect on the mechanical performance of the PVC compounds tested. However, the results show exposure to gamma irradiation had a significant effect on the colour of PVC compounds B, C and D. All three compounds showed significant increases in b-value (yellowness/blueness index) following exposure to gamma radiation. PVC compound A showed superior gamma resistance, with only slight changes in b-value recorded after exposure to gamma irradiation.
Study on the Thermoforming of PC Films Used for in Mold Decoration
Preparation of thermoformed film is one of the critical steps for successful application of mold decoration to parts of complex shape. In the present study, PC films of 0.125mm thick were thermoformed into a cup shape by Drawing Die under various process conditions. Square mark was printed on the surface of film before forming. From the dimension variation of squared mark and thickness distribution of the formed film, one can understand the characteristics of thermoforming. We found the depth of thermoforming increasing will cause wrinkle phenomenon occurrence especially in thinner film. The result indicates that film temperature exhibits the most significant effect on the stretching ratio of the film. Multiple stage of thermoforming was also applied to reduce the residual stress build during forming process and was found to be useful in the reduction of the warpage and wrinkle of the formed film due to the partial relaxation of deformation caused in each stage of forming.
Visual Computer-Based Simulation of the Penetration Length of the Core Melt in Sandwich Injection
The sandwich injection molding technique can be used in wide ranges of engineering applications. On the chance of understanding the melt flow behavior and the mechanism of sandwich injection molding, we made dynamic simulation researches on sandwich injection molding process by employing the software of Moldflow Plastics Insight. In this study, the penetration length of the core melt in sandwich injection molding was investigated by changing the viscosities of melts and process parameters. We find that decreasing the viscosity ratio R of core/skin melts will give rise to enhance the penetration length of the core melt, owing to the relative fluidity of the skin and core melts. Furthermore, the injection velocity of the melts will greatly influence the penetration length of the core melt among the process parameters, while the influences from mold temperature and melt temperature are comparatively inapparent.
Oxypolypropylene as a Radical Initiator for the Production of Polypropylene Grafted Copolymer
Oxypolypropylenes are high MFR propylene polymers that contain bound peroxide functionalities which can be used as polymerization initiators to produce polypropylene grafted copolymers. Upon heat treatment, the peroxides functionalities in the Oxypolypropylene act as a source of free radicals, reacting with unsaturated double bond of the monomers. The grafting reaction is carried out in the solid state in a reactor. The advantage of grafting via Oxypolypropylene is that it eliminates expensive and environmentally unfriendly organic peroxide. A number of monomers have been grafted on Oxypolypropylene, including vinyl acetate, vinyl pyrrolidinone, methacrylic anhydride, maleic anhydride… Applications of these grafted copolymers in nylon blends or in a glass reinforced formulation are also discussed.
Fatigue Behaviour of Two-Layer Materials (PA 6-GF and PP-PET-Fiber, PP or PSU) under Cycle-Dynamic Load
The fatigue behaviour of two-layer materials of glass fiber reinforced polyamide (PA 6-GF) as first layer and polypropylene with polyethylenterephtalat fibers (PPPET- FIBER), polypropylene (PP) or polysulfone (PSU) as second layer is examined by means of the hysteresis measuring method. To determine practice-relevant stress limits for constructional applications fatigue tests with constant and increasing cycle-dynamic load are performed under temperature influence (-40 °C to 82 °C). The experiments have been carried out with a special bending test equipment by means of which a multiaxial stress can be simulated. Microscopic investigations and REM photographs give information on structural failure mechanisms.
PET/PC, PC/PC Flow Properties from Disentanglement Processing (TekFlow)
An extrusion grade PC is mixed with an injection molding grade PET. The mix is alloyed in a Dual TekFlow Processor. A similar procedure is employed on two grades of PC. In each case (PET/PC and PC/PC), the melt is processed at low temperature, low pressure, and under high throughput conditions, made possible by the action of shear-thinning and disentanglement produced by cross-lamination under extensional flow and shear vibration in the TekFlow processors. The melt exiting the TekFlow machine is transparent and homogenous. Analytical testing indicates that the PC/PET alloys present all the characteristics of a molecularly fused new material, exhibiting one Tg, no cold crystallization, no crystallization at all, and a high fluidity. It is shown that the TekFlow PC/PET blends have better flow characteristics than PET. For the PC/PC alloy, it has the same mechanical characteristics as its reference counterparts, at identical Mw.
Characterization of Ternary Blends with Metallocene Copolymers and PA-6
The effectiveness as impact modifier of two maleated metallocene copolymers was studied in ternary blends with polyamide-6 as matrix and two metallocene copolymers as dispersed phase. Also, the effects of the grafting degree on the morphological and tensile properties were investigated. A reduction in tensile modulus and yield stress was observed in all reactive blends and an improvement in adhesion was clearly observed by SEM micrographs. The tensile strength values of blends were lower than that of neat PAs. The results indicated that the effectiveness of the grafted copolymers as impact modifier depend on the morphology of the blends and a combination of tensile properties of the blend components; such as, Young and Poisson’s modulus and break stress of these grafted materials.
Effect of Shear Rate and Mixer Residence times on Morphology Development and Correlation to Young’s Modulus in PS/PP Blends Approaching Co-Continuity
Mixer residence times and shear rates are crucial for development of desired morphologies in polymer blends. Immiscible blends of PS and PP are being studied for development of morphology in a single screw extruder in the co-continuous region. The effect of mixer resident times and shear rates on the morphology development is analyzed. Flexural modulus measurements show strong correlations to selective morphologies obtained at intermediate shear rates and resident times. The influence of morphology on crystallinity of the semi-crystalline phase is considered, and theoretical investigations into the relationships between morphology and mechanics presented.
Dynamic Mechanical Analysis of Polypropylene-Clay Nanocomposites
Polypropylene-clay nanocomposites have become of great interest over the last several years due to their enhanced properties with uncommonly low filler loadings. Dynamic mechanical thermal analysis (DMTA) is a valuable characterization tool because it will give us information about the polymer chain relaxations in the presence of nanoparticles, thermodynamic transitions, and the extent of polymer confinement/clay gallery intercalation. DMTA results are combined with x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy to give a more complete picture of the effect of montmorillonite nanoparticles and a compatibilizer on polypropylene properties.
Effect of Nanoclay on Efficiency of Low Profile Additives (LPAs) on Shrinkage Control of Unsaturated Polyester (UP) Resin
The addition of a small quantity of nanoclay (3 wt%) can greatly enhance the efficiency of low profile additives (LPAs) on volume shrinkage control of low profiled unsaturated polyester (UP)/styrene (St) /LPA systems. In this study, the effect of nanoclay on volume shrinkage of low profiled UP resins containing polystyrene, poly(methyl methacrylate) and poly(vinyl acetate) respectively has been investigated by an integrated approach of static phase characteristics of uncured resin mixture, morphology of the cured samples, reaction kinetics, and shrinkage measurement. The results revealed that nanoclay greatly increased the fraction of LPA-rich phase, leading to a more micro-cracking in the LPA-rich phase or at the interface of the LPA-rich and UP-rich phases, and therefore an prominent improvement of volume shrinkage control. The effect of structure/properties of low profile additives and surface property of nanoclay on shrinkage of UP resin were also investigated.
Rapid Crack Propagation (RCP) Failures in HDPE Pipes: Structure-Property Investigations
The RCP resistance of a wide variety of HDPE pipes was measured using the S4 test, and the relationships between molecular architecture and low-temperature toughness of HDPE pipes are presented. Specifically, we conclude that high molecular weight, high crystallinity and a relatively narrow molecular weight distribution are important. Further, for a given HDPE, our investigations clearly demonstrate that the room-temperature impact energy (razor-notched Charpy Impact test per ASTM F2231) is an inadequate or a poor indicator of the RCP resistance (S4 critical temperature) of the ensuing pipe. However, the ductile-brittle transition temperature, as measured on compression-molded specimens using the razor-notched Charpy impact test, appears to be a reasonably good indicator of the S4 critical temperature of the resultant pipes.
Influence of Branching Distribution on the Physical Properties of High Density Polyethylene
Three sets of two-component blends from various narrow-MWD (molecular weight distribution), linear (no rheologically significant long branches) polyethylenes were prepared with multiple compositions in each set of blends. These blends were deliberately prepared such that the branching (from 1-hexene co-monomer) was present exclusively on either the high or the low molecular weight blend component. In this study, the influence exerted by such selective placement of branching on the physical properties of the resulting blends is discussed. We find that while the instantaneous tensile properties depend exclusively on crystallinity, the ultimate tensile properties depend strongly on branching distribution. Resistance to slow crack growth, impact toughness and the ductile-brittle transition temperature were all noted to depend strongly on branching distribution, with preferential placement of branches along the longer molecules being beneficial. Lastly, the tear resistance and impact toughness of oriented cast films produced using the above blends were also observed to depend on branching distribution.
Analysis of Ductile and Brittle Failures from Creep Rupture Testing of HDPE Pipes
A comprehensive analysis of ductile and brittle failures from creep rupture testing of a wide spectrum of HDPE pipes was conducted. The analysis indicates that the ductile failure of such pipes is primarily driven by the yield stress of the polymer. Examination of ductile failure data at multiple temperatures indicates a systematic improvement in performance with increasing temperature. It is proposed that testing at higher (above-ambient) temperatures leads to progressive relaxation of the residual stresses in the pipe; this causes the pipe to perform better as residual stresses are known to help accelerate the fracture process. Finally, our investigation indicates no correlation, whatsoever, between brittle failures in pressurized pipes and the PENT failure times. Therefore, one has to be extremely cautious in interpreting the true value of the PENT test when developing polymers and pipes for high-performance pressure pipe applications.
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